Wiring method and device

ABSTRACT

To permanently apply lead terminals to corresponding electrodes of electronic or electro-optic components, the following steps are carried out: a. providing a frame including at least one tensioned wire, b. providing a holding jig including at least one seat in which a respective one of the components can be removably and temporarily retained, c. applying the components to the seats with the respective electrodes aligned along a respective longitudinal direction; in this way a row of aligned components is obtained, each component having a corresponding electrode aligned to the subsequent one in the row, d. applying the holding jig to the frame and orienting the same so that the longitudinal direction corresponds to the direction of the tensioned wire, the tensioned wire being thereby brought substantially in contact with (all) the electrode(s) aligned to each other on a corresponding row of components, e. electrically and mechanically bonding the tensioned wire to the corresponding electrodes; in this way all components are simultaneously bonded to the wire, and f. cutting the wire to separate the components from each other thereby forming a respective lead terminal for each electrode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national phase application based onPCT/EP2004/014802, filed Dec. 29, 2004, the content of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wiring method for permanentlyapplying lead terminals to corresponding electrodes of electronic orelectro-optic bipolar components. The invention also relates to a wiringdevice operating according to said method.

TECHNOLOGICAL BACKGROUND

Components adapted to be treated with the method and device of thisinvention include, by way of non limiting example, liquid crystal (LC)cells, including polymer dispersed liquid crystals, condensers,resistors, inductors, particularly of the surface mounting type, thin orthick film hybrid circuits and the like.

Traditionally, terminals suitable to be applied to such components areshaped as electro-conductive wires, strips or lead frames and are welded(brazed) or glued, using electro-conductive glues, onto respectivecontact electrodes. Also known are spring type lead frames such as thosemanufactured by Die-Tec, Inc., 295 Sipe Road—York Haven, Pa. 17370,which are mechanically locked to the electrodes.

The term “wire” in the following context will be used to define anelongated electrically conductive element having any suitable shape toform a lead terminal, including any elongated cylindrical or strip- orband-like shape suitable for this purpose, traditional wires, or leadframes.

Permanent application of “wires” in this technical field is also knownas “wiring”.

Presently known wiring techniques provides for the wiring of a singlecomponent at a time, by applying a layer of conductive glue or solderingpaste over the electrodes, placing and holding appropriate wires incontact with the above mentioned layer and melting the soldering pasteor curing the glue to obtain permanent mechanical and electric bondingof the wires to the electrodes. While these techniques allow highprocess automation and achievement of a reasonable wiring speed, thefact that each component is singularly wired as an individual elementstill remain an evident limitation to a very automated, high throughputwiring process.

U.S. Pat. No. 4,682,563 describes a jig for arraying and supporting amultiplicity of articles to be soldered, such as ICs. This patent ismentioned as background art but it is not pertinent to the invention.

The technical problem at the basis of this invention is that ofproviding a new wiring method for electronic or electro-optic bipolarcomponents by which either one or a plurality of components can besimultaneously wired. Within the general sphere of this problem, it isan important scope of the invention to provide a method applicable todifferent types of components without substantial changes.

DISCLOSURE OF THE INVENTION

Briefly, the method of the present invention, to permanently apply leadterminals to corresponding electrodes of electronic or electro-opticcomponents, comprises the following steps:

-   -   a) providing a frame including at least one tensioned wire,    -   b) providing a holding jig including at least one seat in which        a respective one of said components can be removably and        temporarily retained,    -   c) applying said components to said seats with the respective        electrodes aligned along a respective longitudinal direction; in        this way a row of aligned components is obtained, each component        having a corresponding electrode aligned to the subsequent one        in the row,    -   d) applying said holding jig to said frame and orienting the        same so that said longitudinal direction corresponds to the        direction of said tensioned wire, said tensioned wire being        thereby brought substantially in contact with (all) the        electrode(s) aligned to each other on a corresponding row of        components,    -   e) electrically and mechanically bonding said tensioned wire to        the corresponding electrodes; in this way all components are        simultaneously bonded to the wire,    -   f) cut said wire to separate said components from each other        thereby forming a respective lead terminal for each electrode.

Although the method of the invention is directed to wiring of bipolarcomponents it may happen that only one of the electrodes is wired.Typically, this is the case of radiative RF (Radio Frequency) or MW(microwave) devices such as transmitting and/or receiving antennas orelectronic or electro-optic devices in which the electrode that needs nowiring is represented by an extended metallization on one of the twomain surfaces of the device. Examples thereof are ground-planeelectrodes, sliding contact surfaces, or transducer parts of sensors(i.e. plates for electric charge sensors).

By this method it is possible to mechanically and electrically bond allcomponents applied to a holding jig simultaneously to the tensioned wireor wires so that all components applied to the same jig are connectedwith a corresponding electrode to the same wire which is then cut toseparate the components from each other but leaving a barb of wireattached to the corresponding electrode as a lead terminal thereof.

The components preferably include one or more layers superimposed to oneanother, having at least two electrodes which are set at a distance fromeach other and are substantially parallel to one another. This is thetypical case of bipolar components.

In that case, a corresponding number (at least two) of tensioned wiresare provided on the frame, the wires being set at the same distance fromeach other as the electrodes, so that, when one of said wires issubstantially in contact with one of said electrodes, the other one ofsaid wires is also substantially in contact with the other one of saidelectrodes.

The wording “substantially in contact” is intended to mean, in thiscontext, that the wires are spaced apart from the surface of theelectrodes, when applied thereto prior to bonding, of a distancecomprised between 0 and 200 micrometers.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will appear from thefollowing detailed description thereof given by way of example, withreference to the attached drawings wherein:

FIGS. 1A, B and C are schematic side views of three different types ofcomponents adapted to be wired with the method and device of thisinvention;

FIG. 2 is a top plan view of a first component of the device of thisinvention;

FIGS. 2A, 2B and 2C show particulars on an enlarged scale of the firstcomponent of FIG. 2;

FIGS. 2D and 2E are enlarged perspective views in an assembled andexploded state respectively of the component of FIGS. 2A to 2C;

FIGS. 3 and 4 are respectively a side view and a top plan view of asecond component of the device of this invention;

FIGS. 5 to 7 are respectively a top plan view ad two cross sectionalviews of the device of the preceding figures in two different phases ofthe method of the invention applied to the component of FIG. 1A;

FIGS. 8 and 9 are cross sectional views identical to FIGS. 6 and 7showing the method of the invention applied to the component of FIG. 1B;

FIG. 10 is a cross sectional view identical to FIG. 7 showing the methodof the invention applied to the component of FIG. 1C;

FIGS. 11 and 12 are side views of the device of FIG. 5 when used withthe component of FIG. 1C;

FIG. 13 is a top plan view of a wired component;

FIG. 14 is a perspective partial view of the component of FIG. 13 on anenlarged scale;

FIGS. 15 to 19 are plan views showing the subsequent phases of themethod of this invention.

PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1A through 1C disclose typical configuration of electronic orelectro-optic bipolar components suitable for the wiring method anddevice of this invention. Identical reference numerals indicatefunctionally identical parts.

FIG. 1A shows schematically a cell 1A of the liquid crystal (LC) orpolymer disperse liquid crystal (PDLC) type, including two transparentelectrode-bearing sides 2,3 and a spacer 4 comprised there betweenincluding a LC or a PDLC. For instance, sides 2 and 3 can each comprisea transparent electric conductor, which is capped by a supporting glasslayer. Respective electrode pads 5,6 are formed on each of the sides2,3.

An example of a cell 1A is the assembly of a tuneable mirror such as theone disclosed in U.S. Pat. No. 6,215,928.

The geometry of the cell 1B of FIG. 1B is frequently used in passiveelectronic components (resistors, condensers and inductors) of thesurface mounting type or hybrid circuits (thick or thin film). Electrodepads 5,6 are placed on two opposite longitudinal sides of the cell.

FIG. 1C discloses another possible geometry of a cell 1C provided withcoplanar electrode pads 5,6.

A wired cell of the 1A type is shown at FIG. 13, wherein two leadterminals 15, 16 affixed to the respective electrode surface 5,6 havelead or extensions 17. Similar structure apply to the cells of the 1Band 1C type, when wired.

Wc and Lc respectively indicate the width and length of the cell 1A asshown in FIG. 13. Lw indicates the effective terminal wire length, whiledw is its diameter, assuming that the terminal has a circular crosssection (FIG. 14). Wp and Lp indicate the electrode pad width andlength, respectively. Finally, reference numeral 10 indicates a layer ofsoldering material, i.e., soldering paste or glue, provided onto theelectrode pads 5,6 to electrically and mechanically bond thereto thelead terminals 15, 16. Although generally a layer of soldering materialis applied to the electrode pads, a drop or a ball of soldering materialcan be envisaged in the method of the invention.

A wiring device 100 for applying the lead terminals 15,16 to the cells1A,B,C (herein below jointly referred to as “components”) according tothe present invention includes a frame 101 (FIG. 2) and a plurality ofholding jigs 102 (FIGS. 3 and 4).

The frame 101 (FIG. 2) has a rectangular shape with two oppositelongitudinal legs both indicated by 103, determining a frame length Lf,and two opposite transverse legs 104 and 105, determining a frame widthWf. A plurality of wire pairs 106 a,b are tensioned between thetransverse legs 104, 105 with respective wire ends retained by clampingscrews 106. The term “tensioned wire” in the following context isintended to mean a tensioned electro-conductive element having any shapesuitable to form a lead terminal, including any elongate or strip- orband-like shape suitable for this purpose.

A first seat 107 is provided in leg 104 between each pair of wires 106a,b while a second seat 108 is provided in a corresponding position inleg 105. Seats 107, 108 are aligned to each other and parallel to thewires 106 a,b. The seat 108 includes a sleeve 109 which is slidablyguided on the leg 105 in a direction perpendicular to the leg and wires.The position of sleeve 109 is adjustable by means of a vernier group110. Details of the seat 108, sleeve 109 and vernier group 110 are shownin FIGS. 2D and 2E in an assembled and exploded perspective view,respectively. The sleeve 109 is made by two parts both guided on guidepins 111 perpendicularly to the frame leg 105. The pins 111 are slidablynested in respective guiding grooves 112 one half of which is obtainedin the sleeve outer surface and the other half in a correspondinghousing provided in a centering block 113 which is fitted in the seat108 of the frame leg. The vernier group 110 is mounted on a bridgemember 114 with an adjusting pin 115 thereof urging the sleeve 109against the bias of a spring 116. A pivoting element 117 is mountedwithin an aperture 118 in sleeve 109 held by pins 119 on a pivot axis.

The holding jig 102 (FIGS. 3 and 4) includes a knob 120 at onelongitudinal end and a nose 121 at the opposite end, the nose 121 beingrotatably is received in the pivoting element 117 of sleeve 109 when thejig is mounted to the frame. The jig can be rotated on a longitudinalaxis Y acting on the knob 120, a marker 122 being provided on the knobto indicate the position of the jig relatively to the frame duringrotation thereof.

The jig includes a shaft 123 having a plurality of seats 124 in the formof transverse notches. The seats 124 are intended to receive each acorresponding component or cell 1A, B, or C, all components being of thesame type, shape and dimensions.

An insert 125 is provided on the shaft 123 at the knob side, the insert125 being shaped so as to self-centering fit into the first seat 107 ofthe frame. Each seat 124 has a bottom provided with a releasablyretaining element such as a suction duct 126 connected to a suctionchannel 127 extending through the jig and terminating at a suction valve128 by means of which said channel can be connected to a vacuum sourcesuch as a vacuum pump. Means other than suction can be however used toretain the components 1A, B, or C in the seats 124, such as an adhesivelayer covering the bottom of seats 124 or mechanical retaining meanssuch as clips and the like.

According to the method of this invention, the frame is first “wired” byfixing thereto a plurality of tensioned wires by means of clampingscrews 106; meanwhile a soldering material is applied to the electrodepads of each cell to be wired.

It has been noted that the volume of the soldering material will dependon the dimension of the surface of the electrode pads as well as fromthe volume of the section of wire extending over the pad surface:preferably the soldering material shall be applied so as to cover notless than 60% of the surface of each electrode pad and the volumethereof shall be 1 to 4 times the volume of the section of wireextending over the pad surface. Higher volumes of glue used as solderingmaterial may cause percolation and/or contamination of other surfaces.

Appropriate glues are conductive epoxies. Examples thereof are TRA-DUCT2902 or TRA-DUCT 916H03 by TRACON Inc. (45 Wiggins Avenue, Bedford,Mass. 01730-USA) or AGAR Acheson Silver DAG 1415M or similar. Theseglues are then baked with baking parameters spanning from 24 hours at25° C. to 1-30 minutes at 180° C. as will be made clear hereafter withreference to the baking phase.

In case of soldering techniques, it is a first requirement that theelectrode pad surface be metallurgically compatible with the wire.Examples are pads made of Cu, Ti also coated with a plurality ofcoatings such as Pd, Ni, Au, with wires of Cu, Fe—Ni alloys or Zn, withappropriate soldering materials such as Sn, Pb In and Ag, alloys.

An eutectic alloy known as INDIUM ALLOY #290 In 97% Ag3% melting at 143°C. has been used successfully.

Due to the thermal sensitivity of liquid crystals, technologicalprocesses that include baking at relatively high temperatures aregenerally avoided. The maximum temperature that a LC cell can bearwithout being damaged depends of course on the type of LC (or PDLC) andon the baking time.

The soldering parameters shall be preferably chosen as follows.

A preferred baking temperature range is 118 to 280° C., depending on theis volume Vc and thermal mass of the cell. The higher is the thermalmass of the cell the lower shall be the baking temperature. It has beennoted that for volumes Vc of 50 mm³ or lower, a baking temperature of280° C. for a baking time of 5 seconds is preferable; for Vc comprisedbetween 50 and 250 mm³ baking temperature and time shall be adjusted to180° C. and 5 minutes respectively; for Vc comprised between 250 and1000 mm³ baking temperature and time shall be adjusted to up to 150° C.and 60 minutes, preferably.

Particular in case of LC cells, baking time is selected depending alsoon the baking temperature. For instance, at baking temperature of 280°C., the baking time should preferably not be higher than a few seconds,e.g., 5 s.

With INDIUM ALLOY #290 In 97% Ag3% melting at 143° C. as solderingmaterial, wires size of 100 micrometers in diameter and cells having avolume of 70 mm³ no derating of the cell occurred even with long bakingtimes (ex. 120 minutes).

As far as the frame, wires and cell parameters defined above areconcerned, it has been found that the following relationships preferablyapply.

-   0.1 Wc≦Lc≦10 Wc-   Lc≦Lw≦20 Lc-   0.1 Wp≦D≦0.8 Wp-   Wp≦Lp≦10 Wp

The frame shall be organised to accept a number of jigs between 1 and100 and a corresponding number of wire pairs.

The distance (or pitch) between the wires 106 a,b of each pair shall besubstantially identical to the distance between the electrode pads 5, 6of the cell. With particular reference to the component of FIG. 1A, thethickness of the cell spacer 4 shall determine the offset, if any,between the wires 106 a,b of each pair.

The frame length Lf is critical for a proper tension of the tensionedwires. A satisfactory ratio between Lf and the wire diameter dwrespecting the elongation characteristics of most commonelectro-conductive wiring materials (including Au and Ag) is given bythe following empiric formula:

-   Lf/dw=1000 for 50 μm<dw<350 μm-   Lf/dw=1500 for 350 μm<dw<800 μm-   Lf/dw=1850 for 800 μm<dw<1000 μm

Typical dimension of frames may vary from 0.001 m² to 2 m² and abovewith a number of cells per frame from 1 to 1000.

An important feature of this technology is that the frames may besuperimposed to one another thereby obtaining a multi-layer structurewhich allows space saving.

Dimensional stability of the frame is also important, particularly asfar as the camber of the legs under the tension of the wires isconcerned. A camber of each leg of less than 1/800 on the length of theleg itself was found satisfactory, the camber being measured at themaximum temperature at which the frame can be exposed during baking ofthe glues or soldering paste.

Frames having an area of 0.04 m² and up to 2 m² or above are preferablymade of metals, (also as a section bar) such as aluminium and itsalloys, Fe—Ni alloys (es. Kovar, Invar, etc.), brass, steel, etc.

For lower area frames an economically more affordable solution could berepresented by extruded or moulded plastics chosen from technicalpolymers having high dimensional stability such as ABS, glass-fillednylon, polycarbonates, and similar.

Once provided both frame 101 and jigs 102 and wired the frame, the jigs102 are loaded with cells by positioning each cell in the respectiveseat 124 so that the electrode pads 5,6 are aligned to each other alongtwo longitudinal directions parallel to the jig axis Y.

Either prior to loading cells into the jigs or immediately thereafterbut anyway prior to inserting the jigs into the frame, the glue orsoldering paste is applied to the electrodes.

The jigs are then inserted into the frame.

For jigs bearing cells of the 1A or 1B type the jig is first inserted inthe frame standing on edge, as shown in the upper part of FIG. 5 or FIG.6 (cells 1A) or in FIG. 8 (cells 1B) and than rotated by 90° or less,depending on the thickness of the cell, until the electrode pads arebrought substantially in contact with the wires 106 a,b. (lower part ofFIG. 5 and FIG. 7 for cells of the 1A type and FIG. 9 for cells of the1B type)) Substantially in contact is intended to mean that the wires bespaced apart from the respective pads of a distance comprised between 0and 200 μm. For cells of the 1C type, the jig is inserted into the frameas shown in FIGS. 11 and 12, first nesting the nose 121 into the sleeve109 and then pivoting the jig and sleeve so as to lower the knob 120toward the frame 101. In this way the wires 106A,B are brought intosubstantial contact with the electrodes 5,6, the contacting conditionsbeing adjustable by means of the vernier 110.

The system is then placed in a heated environment to cure the glue ormelt the soldering paste as taught above. This step is generallyindicated as “baking”.

Mechanical and electrical bonding of the wires to the electrode pads isthereby obtained.

Then the pair of wires are cut close to the respective frame legs (FIG.15), the jigs are removed from the frame (FIG. 16) and the set of cellsattached to each other in parallel, in a sort of chain, are removed fromthe jigs by closing the suction valve 128. This step is shown in FIG.17.

To singularise the wired components, the wires 106 a,b are cut close tothe same side of each cell, as indicated by a cross in FIG. 18,according to the wiring design needed.

The singularised components 1A,B or C provided with wirings,comprehensively indicated by 130 in FIGS. 13 and 19 are then ready fortest and packaging.

1. A method to permanently apply lead terminals to correspondingelectrodes of electronic or electro-optic components comprising thesteps of: a. providing a frame comprising at least one tensioned wire;b. providing a holding jig comprising at least one seat in which arespective one of said components can be removably and temporarilyretained; c. receiving said components in said at least one seat withthe respective electrodes aligned along a respective longitudinaldirection, such that said components are retained in said jig; d.receiving said holding jig retaining said components in said frame andorienting the same so that said longitudinal direction corresponds tosaid tensioned wire and said at least one tensioned wire issubstantially in contact with said electrodes; e. electrically andmechanically bonding said tensioned wire to the correspondingelectrodes; and f. removing said components from said at least one seatand cutting said tensioned wire to separate said wired components fromeach other thereby forming a respective lead terminal for eachelectrode.
 2. The wiring method according to claim 1, wherein saidcomponents have each at least two electrodes which are set at a distancefrom each other and wherein at least two tensioned wires set at the samedistance from each other are tensioned in said frame.
 3. The wiringmethod according to claim 2, wherein the at least two electrodes are twoelectrodes and the at least two tensioned wires are two tensioned wires,and wherein said holding jig and said tensioned wires are reciprocallydisposed so that, when one of said tensioned wires is substantially incontact with one of said electrodes, the other one of said tensionedwires is also substantially in contact with the other one of saidelectrodes.
 4. The wiring method according to claim 1, wherein aplurality of seats is formed on said holding jig to receive acorresponding plurality of components aligned in a row extendingparallel to said longitudinal direction.
 5. The wiring method accordingto claim 4, wherein said components are removably held in positionwithin the respective seats in said holding jig by means of air suctionapplied between said seats and the component received therein.
 6. Thewiring method according to claim 1, wherein the step of bondingcomprises applying a soldering material to said electrodes and bringingsaid tensioned wires in contact with said soldering material.
 7. Thewiring method according to claim 6, wherein bringing said tensionedwires in contact with said soldering material is followed by baking saidsoldering material at a baking temperature to permanently attach saidtensioned wires to said electrodes.
 8. The wiring method according toclaim 6, wherein said tensioned wires are brought in contact with saidsoldering material at a distance from the respective electrodes of 0 to100 microns.
 9. The wiring method of claim 7, wherein said solderingmaterial is a soldering paste and baking comprises melting of thesoldering material.
 10. The wiring method according to claim 9, whereinthe soldering material for the bonding of the tensioned wires is a Sn,Pb, Ag, or In based alloy.
 11. The wiring method according to claim 10,wherein said soldering paste is a eutectic indium alloy comprising In97% Ag3%.
 12. The wiring method according to claim 1, wherein saidelectrodes are made of a Cu, Ti pad.
 13. The wiring method according toclaim 1, wherein said tensioned wires comprise Cu, Fe—Ni, or Zn andcorresponding alloys.
 14. The wiring method according to claim 12,wherein said electrodes are coated with coatings chosen from Pd, Ni, andAu.
 15. The wiring method according to claim 7, wherein said bakingtemperature is 118° to 280° C.
 16. The wiring method according to claim15, wherein said baking temperature is maintained for a baking time ofless than 2 hours when said baking temperature is between 143° C. and280° C.
 17. The wiring method according to claim 16, wherein said bakingtime is progressively decreased from 2 hours to 5 seconds when saidbaking temperature is increased from 143° to 280° C.
 18. The wiringmethod according to claim 15, wherein the baking temperature isinversely proportional to the volume of the component.
 19. The wiringmethod according to claim 18, wherein for a component volume of lessthan 50 mm³, the baking temperature and time are respectively up to 280°C. and 5 seconds, for a component volume of 50 to 250 mm³, the bakingtemperature and time are respectively up to 180° C. and 5 minutes, whilefor a component volume of 250 to 1000 mm³ the baking temperature andtime are respectively up to 150° C. and 60 minutes.
 20. The wiringmethod according to claim 6, wherein the soldering material is disposedover the corresponding electrodes to cover not less than 60% of theelectrode surface.
 21. The wiring method according to claim 7, whereinthe volume of the soldering material is 1 to 4 times the volume of thesection of tensioned wire laying over the surface of the electrode to beconnected thereto.
 22. The wiring method according to claim 7, wherein abaking temperature of 25° to 180° C. and a baking time of 1 minute to 24hours are applied during the baking phase of said soldering material.23. The wiring method according to claim 1 wherein said jig is insertedin the frame standing on edge and then rotated relative to the frameuntil the electrodes are brought substantially in contact with thetensioned wires.
 24. The wiring method according to claim 1, whereinsaid jig is inserted into the frame by nesting a nose at one axial endthereof into a sleeve pivotally mounted on the frame and then pivotingthe jig and sleeve so as to lower an opposite axial end of said jigtoward the frame, thereby bringing the electrodes into substantialcontact with the said tensioned wires.